(1) Field of the Invention
The present invention relates to a method and system for delivering radiation treatments to cancerous tissues within the human pelvis, such as the prostate gland and the cervix, while avoiding tissues that would otherwise be damaged by aggressive radiation treatment.
(2) Description of Prior Art
Radiation therapy and radiosurgery are established methods of treating patients with certain malignant and benign diseases. Radiotherapy is typically given over many episodes of treatment and generally involves treating larger volumes of tissue that often include normal structures that may be affected adversely by the radiation treatment. The strategy of spreading the therapy over many episodes separated in time is chosen to enable recovery of normal tissues included in the treatment volume. It is assumed that recovery of normal tissue occurs at a faster rate than that for cancerous tissue. Radiosurgery is typically given in one or a few episodes of very precise treatment to small volumes of diseased or affected tissue with the intent to destroy all tissue contained within the treatment volume.
Toxicity to normal structures limits the radiation dose and the treatment efficacy of both methods as normal structures may be contained within or adjacent to the diseased tissue. A normal structure within the prostate gland is the urethra. The normal tissues in proximity to the prostate gland are illustrated in FIGS. 2 & 3 and include but is not limited to the bladder and rectum as well as femoral heads and small intestine.
Prostate cancer is known to be slow growing and resistant to conventional treatment which is given by applying many small doses of radiation. Hypofractionation or a few large doses of radiation has been demonstrated to be more effective in killing cancerous cells for the same amount of energy deposited. However this approach causes unacceptable toxicities such as urethral stricture or even tissue necrosis. Although in theory we know that a higher daily dose is more effective for curing prostate cancer. However, daily dose greater than a 3Gy dose using external beam radiation has not been widely used because of urethra necrosis. Martinez et al. used radioactive seeds interstitially introduced to the prostate to deliver more than 10.5Gy daily dose to prostate and was found to be very effective. Vicini et al., High Dose Rate Brachytherapy In The Treatment Of Prostate Cancer, Journal World Journal of Urology, vol. 21, no. 4 (Sept. 2003), pp 220-228.
Because Vicini et al. used “peripheral loading”, i.e., placing more radioactivity at the periphery of the prostate and avoiding high dose to the urethra, the toxicity from their interstitial high dose rate treatment was found to be low. However, their method has the greatest detriment of being very invasive and must be performed under general anesthesia. The present inventors do not know any method that can safely deliver a daily dose of greater than 3Gy using external beam radiation without damaging the urethra. Note that, although prostate cancer is used as an example, the method disclosed in this invention is not limited to the treatment of prostate cancer. There has not been any method that can safely deliver a high dose to the target while sparing a critical structure completely surrounded by cancerous tissue.
There is no treatment machine that can optimally spare the urethra and other critical organs such as rectum and, bladder and seminal vesicles. Conventional Modern radiotherapy employing intensity modulation techniques provides better dose conformity to the prostate and less dose to the bladder and rectum, with a typical dose distribution illustrated in FIG. 4, has enabled higher doses to the prostate by limiting the dose to structures surrounding the prostate but still gives high doses to the urethra. Therefore, hypofractionated radiation treatment for prostate cancer remains a dangerous procedure. For practical reasons such as treatment time and machine geometry, conventional treatment further has the limitation of approaching the prostate from a small solid angle and typically only transverse coplanar beams are used.
There is no dedicated tele-radiotherapy machine specifically designed to treat prostate cancer using a single or an arrangement of radioisotopes or other source of high energy radiation.
Protons have also been used for prostate treatment. This is an extremely expensive and complex method and has not demonstrated any benefit in part due to the challenges mentioned above for conventional treatment.
Past efforts of intensity-modulated radiation therapy have been limited to the use of compensators or multi-leaf collimators to modulate the incident radiation beams. The treatment beam arrangement is generally coplanar with the axis of rotation in the cranial caudal dimension.
In the present application the inventors describe a treatment device with unique beam geometry and collimation technology that can sculpt a radiation pattern avoiding the urethra and bladder and rectum while covering the prostate gland with a higher radiation dose.
Similar past efforts in image guidance have been limited to pretreatment imaging or treatment monitoring using simple planar X-ray fluoroscopy. Pretreatment imaging can include ultrasound, CT scanning, MRI and MV or kV planar X-ray. In the case of pretreatment imaging the tissues are not represented in real time during the treatment and changes that occur are not observed. In the case of X-ray fluoroscopy at the time of treatment imaging is limited to boney landmarks or implanted markers as surrogates for target tissues. In this invention we outline a technology and method to detect and monitor relevant soft tissue interfaces during radiation treatment.
Radiation therapy using external beams as described above and illustrated in FIG. 4 typically places the tumor at the isocenter, the intersection of all rotational axis. This arrangement makes patient set-up much easier. However, at any beam direction, radiation can only be directed at a point in the tumor through one unique path. This significantly limits the degree of freedom of how the tumor is irradiated. In this disclosure, we abandon the notion of a single isocenter and expand the control parameters of the treatment delivery to include the position of the treatment couch, which is fixed in all existing radiation treatments. The beams and the collimator still rotate around a point, but this point is no longer fixed in the patient. Thus, there is an abandonment of fixed isocenters inside the patient. Instead, maintaining a source rotational isocenter in the device is one of the key features of the present disclosure, a feature that has not been proposed or explored in radiation therapy.
Important features of the invention also include a practical method for real-time monitoring of the location of the critical structures and real-time adjustment of treatment parameters to spare these critical structures. This is again achieved through the extension of the definition of control points by associating with each control point a critical point of reference, which is a landmark on a critical structure that needs to be protected. For prostate treatment, we propose the use of an endorectal ultrasound probe to monitor the position of key interfaces, namely the urethra and the anterior rectal wall. For every control point that defines the treatment parameters at one time interval, there is a unique critical point of reference, which is normally the closest interface location. During delivery, the reference point for the next control point is updated during the delivery of the current control point based on the real-time imaging and real-time registration of the interface features between that acquired in real-time and that used for planning the treatment. Such updating of the locations of critical interfaces as the geometric reference of the control points allows the treatment to adapt to anatomy changes to protect the critical structures without changing the treatment plan.
Numerous clinical reports have established that the effects of radiation on urethra is a long-term process and the incidents of late effects increases with time over 20 years without a plateau. See, e.g., Miller et al., “Long-Term Outcomes Among Localized Prostate Cancer Survivors: Health-Related Quality-Of-Life Changes After Radical Prostatectomy, External Radiation And Brachytherapy”, Journal of Clinical Oncology (Vol. 23, No. 12: 2772-2780). The slope of increase is directly proportional to the fractional dose delivered to the urethra. To date, there is no radiation treatment machine that can deliver high doses of radiation to the prostate while being able to spare the urethra.
In view of the foregoing, it is an object of the present disclosure to provide a method and an external irradiation system for delivering high doses of radiation to lesions within the human pelvis, such as the prostate, while sparing its surrounding structures, such as the rectum and bladder, as well as the urethra that is contained inside the prostate. The system would allow the radiation to be directed from a large number of beam directions through the arrangement of radiation sources and through the rotation of the radiation sources around the patient so as to achieve the maximal “cross-firing” effect. The system will also allow the treatment support structure to move dynamically so that the paths of the rays can optimally traverse the target in order to avoid the critical structures both internal and external to the target.
All radiation therapy treatment machines currently used for external beam radiation treatment are designed in such a way that the machine can deliver radiation to all tumor locations from a patient's head to a patient's toe. Such versatility is partly the reason that all external treatment machines used for irradiating prostate cancer externally uses only one radiation source. Although the source can be moved around to achieve “cross-firing” effect, practical considerations, such as the total treatment time and patient safety, limit the number of directions that the treatment can employ. Moreover, because all external beam treatment devices, such as the linear accelerators and Co-60 teletherapy machines, have a large treatment head required for shielding and collimation purposes, many beam angles cannot be used without causing a collision between the head of the machine and the patient.
In view of the above, we disclose a radiation machine design that utilizes a plural number of radiation sources arranged specifically for irradiating tumors in the human pelvis. In order to utilize all potential beam directions while not harming critical structures, the machine also contains motorized shields for different sensitive structures, including the rectum, femoral head, bladder, kidney, and testis. For different patients, these structures will be revealed by the three-dimensional images, such as CT and MRI, and the locations of these shields can then be customized for each individual patient.
It is well documented that the prostate gland changes location and shape within the pelvis relative to boney or surface landmarks between planning and treatment events. It is also recently documented that the prostate gland may change location and shape significantly during a typical 2-10 min episode of conventional radiation treatment. Court et al., Motion And Shape Change When Using An Endorectal Balloon During Prostate Radiation Therapy, Radiotherapy and Oncology, Volume 81, Issue 2, Pages 184-189.
Image Guided Radiation therapy today is limited to one of pretreatment ultrasound, planar x-ray, computed tomography or during treatment fluoroscopy. These approaches are used to define relative positions of internal structures to the radiation treatment isocenter using surrogates. Treatment fluoroscopy is limited to tracking implanted markers or boney landmarks and implementations generally have poor response times and so cannot be used to directly drive treatment or treatment modification. A key feature of the image guidance approach for this invention is that the device will use a combination of full 3D imaging, which require longer processing and feedback time, and boundary imaging, which only process and compare a small subset of the imaging signals for fast, real-time comparison and feedback. For the latter, only the tissues that define the boundary of the target and normal structure that we wish to avoid are imaged. The benefit of limiting the number of full 3D image acquisition and processing and only focusing on the interface between the target and the critical structure is the possibility to monitor the change in location and share of such critical interface in real-time. Such real-time monitoring would allow us to adapt the planned irradiation to such changes by changing the radiation beam angle and position relative to such boundaries. It will thus be possible to respond to any inadvertent or intended motion as part of the overall quality assurance of the treatment.
Other features, advantages and characteristics of the present invention will become apparent after the following detailed description.